Water is the universal solvent, pure water is non-existent in nature due to its dissolving properties. The contamination of drinking water has become one of the major environmental issues of the present era. Organics are one of the major source of contaminants in drinking water. They are derived from the decomposition of plants and animals,natural organics, synthetic organics, both industrial and agricultural pollution and the reaction of organics during water treatment. Based upon the data collected fifty different pesticides and six halogenated organic chemicals have been detected in the wells that are one of the prime sources of domestic water supply. The most ubiqitous synthetic organic compounds found in drinking water are the trihalomethane, predominantly chloroform, the by-product of water treatment when chlorine reacts with natural organic materials including aquatic humic material in water. The range of organic compounds in drinking water amounts to hundreds, however most of the organic components in drinking water are non-volatile substances with molecular weights in excess of 1000.
Regarding inorganic contaminants besides the most harmful arsenic, cadmium, lead, mercury and chromium, the naturally occuring asbestos and selinium have been found in some of the urban water systems. Nitrates formed by oxidation of ammonium ions with microorganisms in water, is one of the most common contaminants in agricultural areas.It is a well establiched fact that a large number of the contaminants in drinking water have harmful health effects. Although carcinogenic effects of some of the contaminants in the water have been established, the long term harmful effects of the wide variety of these contanimants in the drinking water is difficult to comprehend.
A large number of microorganisms also occur as contaminants in the drinking water. The human health implications of microbiological contamination of water are more severe than that of chemical contamination.The aquatic microbiology are diverse and include bacteria, virus, algae, fungi, and protozoa, and their size is an important factor in their treatment and removal.
Another source of contaminants of significant harm to human health are finely divided and suspended particles from soil, silts, sediments colloids and asbestos fibres in drinking water.
In view of the fact that drinking water containing numerous contaminants, the adverse health effects of some of which are known, and majority of them are yet unknown, it is imperative that water for human internal consumtion must undergo purification at the point of use.